Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

Show paginator

Hide paginator

25%

Page 1 of 4

1. The boiling point of ammonia is

-77.7°C

-30°C

-10.5°C

-33.3°C

2. In a flooded evaporator refrigerator, an accumulator at suction of compressor is used to

Detect liquid in vapour

Superheat the vapour

Collect vapours

Collect liquid refrigerant and prevent it from going to compressor

3. A human body feels comfortable when the heat produced by the metabolism of human body is equal to the

(A) Heat dissipated to the surroundings

(D) Difference of (A) and (B)

(B) Heat stored in the human body

4. The value of C.O.P in vapour compression cycle is usually

Any one of the above

Equal to unity

Always less than unity

Always more than unity

5. On the pressure-enthalpy diagram, condensation and desuperheating is represented by a horizontal line because the process

Takes place at constant temperature

Involves no change in volume

Takes place at constant pressure

Takes place at constant entropy

6. The refrigerant after condensation process is cooled below the saturation temperature before throttling. Such a process is called

Super-cooling

Sub-cooling or under-cooling

Normal cooling

None of these

7. The freezing point of sulphur dioxide is

-135.8°C

-77.7°C

-75.2°C

-56.6°C

8. In actual air-conditioning applications for R-12 and R-22, and operating at a condenser temperature of 40° C and an evaporator temperature of 5° C, the heat rejection factor is about

5.12

1.25

2.15

9. A bootstrap air cooling system has

Four heat exchangers

One heat exchanger

Three heat exchangers

Two heat exchangers

10. The vapour compression refrigerator employs the following cycle

Carnot

Rankine

Reversed Rankine

Reversed Carnot

Page 2 of 4

11. Critical temperature is the temperature above which

Water will evaporate

Water will never evaporate

A gas will immediately liquefy

A gas will never liquefy

12. The minimum temperature to which water can be cooled in a cooling tower is

Ambient air temperature

Dew point temperature of air

Wet bulb temperature of air

Dry bulb temperature of air

13. Rating of a domestic refrigerator is of the order of

10 tons

5 tons

0.1 ton

40 tons

14. The atmospheric air at dry bulb temperature of 15°C enters a heating coil maintained at 40°C. The air leaves the heating coil at 25°C. The bypass factor of the heating coil is

0.6

0.4

0.376

0.67

15. Which of the following cycles uses air as the refrigerant?

Bell Coleman

Stirling

Carnot

Ericson

16. The general rule for rating refrigeration systems (excepting for CO₂ system) is to approximate following h.p. per ton of refrigeration

0.5 to 0.8 h.p. per ton of refrigeration

1 to 2 h.p. per ton of refrigeration

0.1 to 0.5 h.p. per ton of refrigeration

2 to 5 h.p. per ton of refrigeration

17. A thermostatic expansion valve in a refrigeration system

None of the above

Ensures the evaporator completely filled with refrigerant of the load

Maintains different temperatures in evaporator in proportion to load

Is suitable only for constant load systems

18. Freon group of refrigerants are

Toxic

Non-inflammable and toxic

Nontoxic and non-inflammable

Inflammable

19. The capillary tube, as an expansion device, is used in

Domestic refrigerators

Room air conditioners

All of these

Water coolers

20. The C.O.P. of a refrigerator working on a reversed Carnot cycle is (where T₁ = Lowest absolute temperature, and T₂ = Highest absolute temperature)

(T₁ - T₂)/T₁

(T₂ - T₁)/T₁

T₁ / (T₂ - T₁)

T₂/ (T₂ - T₁)

Page 3 of 4

21. Which of the following is not a desirable property of a refrigerant?

Low boiling point

Good electrical conductor

High risibility with oil

Large latent heat

22. When the temperature of the surrounding is higher than the temperature of the body, then the heat loss by convection from the body to the surrounding will be

Zero

Negative

Positive

None of these

23. The condition of refrigerant after passing through the condenser in a vapour compression system is

Superheated vapour

Dry saturated vapour

Wet vapour

Saturated liquid

24. Which of the following statement is correct?

(D) Both (A) and (B)

(B) The increase in air movement increases the evaporation from the human body.

(A) The human body can lose heat even if its temperature is less than the atmospheric temperature.

25. Most thermostatic expansion valves are set for a superheat of

20°C

5°C

15°C

10°C

26. For obtaining high COP, the pressure range of compressor should be

Optimum

High

Low

Any value

27. If a heat pump cycle operates between the condenser temperature of +27°C and evaporator temperature of -23°C, then the Carnot COP will be

0.2

1.2

28. In a refrigeration system, heat absorbed in comparison to heat rejected is

Less

Same

More for small capacity and less for high capacity

29. The curved lines on a psychrometric chart indicates

Relative humidity

Wet bulb temperature

Dry bulb temperature

Dew point temperature

30. The change in evaporator temperature in a refrigeration cycle, as compared to change in condenser temperature, influences the value of C.O.P.

Unpredictable

Less

Equally

Page 4 of 4

31. The domestic refrigerator uses following type of compressor

Centrifugal

Piston type reciprocating

Miniature sealed unit

Axial

32. Highest temperature encountered in refrigeration cycle should be

Above critical temperature

At critical Temperature

Near critical temperature of refrigerant

Much below critical temperature

33. Cooling water is required for following equipment in ammonia absorption plant

Absorber

Condenser, absorber and separator (rectifier)

Evaporator

Condenser

34. The operating pressure for refrigerating units using R-12 as a refrigerant is

8 bar

2 bar

15 bar

30 bar

35. In a refrigeration system, the expansion device is connected between the

Condenser and receiver

Compressor and condenser

Receiver and evaporator

Evaporator and compressor

36. In a lithium bromide absorption refrigeration system

Water is used as a refrigerant and lithium bromide as an absorbent

Ammonia is used as a refrigerant and lithium bromide as an absorbent

Lithium bromide is used as a refrigerant and water as an absorbent

None of these

37. A reversible engine has ideal thermal efficiency of 30%. When it is used as a refrigerating machine with all other conditions unchanged, the coefficient of performance will be

4.33

3.33

2.33

1.33

38. Mass flow ratio of NH₃ in comparison to Freon-12 for same refrigeration load and same temperature limits is of the order of

9: 1

1: 1

1: 3

1: 9

39. A certain refrigerating system has a normal operating suction pressure of 10 kg/cm gauge and condensing pressure of about 67 kg/cm. The refrigerant used is

Ammonia

Carbon dioxide

Freon

Brine

40. The bank of tubes at the back of domestic refrigerator is

Condenser tubes

Capillary tubes

Refrigerant cooling tubes

Evaporator tubes

Share this Now with Friends:

VideRime

A Demrot is the founder of VideRime Online Learning, a leading engineering website. He did his BE Civil and M.Tech Structure from RGPV University, Bhopal and has been working as an Assistant Professor in a reputed college.

Refrigeration & Air-Conditioning Practice Set-3

Related

Leave a ReplyCancel reply

Ads by Google

Recent Posts

Membership Registration

Secured Payment

Protection